The T-stat is right next to the water pump. Since he is removing the water pump it would be extremely silly not to change the T-stat. Plus, you have to remove the water pump to change the T-stat. IMO, why don't you just check everything since the X will be at the mechanic? Maybe shell out some extra $$$ and get spark plugs, valve covers, T-stat, Oil breather hoses. That's if you haven't changed them already. Have fun...